Vegetable Oil Refining and Waste Water
Vegetable oils are natural fats which occur in the seeds of oil-seed plants such as soybean, cotton, corn and sunflower.
The oils are solvent extracted and refined for edible use as cooking oil (e.g., Wesson Oil.TM.), shortening (e.g., Crisco.TM.), salad dressings, mayonnaises and margarines.
Vegetable oil refining essentially involves the removal of free fatty acids (FFA) and gums (to a lesser extent) from the crude oil. Gum removal is sometimes facilitated by addition of traces of phosphoric acid. The refining is accomplished by mixing the oil with a hot, aqueous caustic solution (sodium hydroxide) and centrifugally separating the reaction products from the "refined" oil. The waste product, an alkaline mixture of saponified FFA and gums is referred to as soapstock.
The soapstock waste has commercial value, because of the fatty acid content as a high energy seed supplement, but must be processed further in order to render it salable. Processing simply amounts to breaking or splitting the soap into oil and water again by adding acid (Sulphuric acid) to approximately pH 1.5. After heating and mixing thoroughly, the acidulated soapstock is allowed to settle out. The oil that floats to the top is called "acid oil" and is drawn off for sale usually as an animal feed supplement. The aqueous phase remaining is termed "acid water". Acid water is the final waste product and is discarded. However, there is a disposal problem. Acid water contains all the undesirable and objectionable pollutants of the refining process. Sewer authorities at a bare minimum require that the acid water be neutralized (NaOH is added) before the waste is allowed to be dumped. Some states have more stringent pollution control and have forced companies out of business because of acid water disposal.
Thus, in the conventional refining of vegetable oils, sodium hydroxide is used as the refining base, sulfuric acid used to acidulate soapstock and sodium hydroxide again employed to neutralize acid water.
Although established and inexpensive, this technology results in a waste product that, due to environmental legislation, has become increasingly difficult and costly to dispose of.
Since all of chemicals used to refine, acidulate and neutralize together with the undesirable constituents of crude oil, gums etc., are found in concentrated form in the acid water, examination of acid water will show it to be high in BOD, soluble salts and phosphorus. The soluble salts are primarily sodium sulfate and sodium phosphate. The sodium comes from the refining base (NaOH) and the acid water neutralizer (NaOH); the sulfate from the acidulating acid (H.sub.2 SO.sub.4); the phosphorus from naturally occurring phosphatides (gums), which are hydrolyzed during acidulation into phosphate, and pretreat or process additions of phosphoric acid. Plant protein and carbohydrate fragments together with glycerol and residual oil produce the high BOD levels.
Enactment of environmental legislation has caused the disposition of soapstock and, in particular, acid water to become an increasingly difficult and costly problem. Not only is acid water highly acidic, it is high in b.o.d. and phosphorus. Several localities have strict effluent standards which force refiners to ship soapstock to an area with more liberal regulations where it can be acidulated.
In 1982 a privately funded research program was initiated to attempt to discover novel treatment processes for a large volume industrial waste product, the disposal of which had gained the attention of the Environmental Protection Agency (E.P.A.).
Phosphorus, the main component of the industrial waste, was creating a pollution problem which gained national and international attention--the eutrophication of a valuable natural resource, rivers and lakes. The E.P.A. focused on the problem and many plants/businesses were forced to close for non-compliance with the Federal Water Pollution Control Act (Clean Water Act) of 1972 and amendments of 1977 and 1981.
Additional emphasis was placed on the waterways of the Great Lakes Basin area of the U.S. and Canada. The Great Lakes Water Quality Agreement of 1978 was signed and the International Joint Commission was established by the United States and Canada. The new Agreement reinforces the importance of controlling phosphorus pollution. The importance of this continuing effort to enforce stricter standards is of special concern, since the Great Lakes region has one of the highest densities of industries that generate the waste product in the world.
At present, there is no treatment technology available to industry that will meet proposed E.P.A. standards.
According to a recent statement by W.R. Grace Company:
"In an effort to address the environmental concerns that this industry faces, W.R. Grace is pioneering a new refining technology-Modified Caustic Refining (MCR). PA0 MCR utilizes TriSyl's ability to adsorb significant quantities of phosphatides and soap, thereby eliminating the need for the water wash centrifuge step. Elimination of this unit operation results in lower wastewater treatment costs, and improved adsorbent utilization."
This demonstrates the importance of environmental concerns that the vegetable oil industry is facing.
W.R. Grace is promoting a method that reduces the remaining soap and phosphatides from once refined oil that previously was removed by a water wash, which shows that the industry struggles to find a cost efficient technology or method, or any technology, that prevents or minimizes the residual amounts of soap and phosphatides from the environment.
A recent issue of Water Pollution Control Facilities magazine further indicates the general doctrine of water pollution control: that the so-called "nutrients" (nutrients apparently relate to the extent that the component causes undesirable plant growth in waste water streams) is an undesirable nuisance which must be removed from the waste water stream using sophisticated separation techniques. This feeling in the pollution control art probably derives from the fact that the fundamental doctrine of those now working in the waste water field is that waste water is something that is supposed to be ejected from the system. This narrow-minded doctrine probably derives from the inbred historical paranoia in western civilization concerning waste water.